Process for refining pressure distillate



April 15, 1941. D. G. BRANDT PROCESS FOR REFINING PRESSURE DISTILLATE Filed Oct. 23. 1937 Patented Apr. 15, 1941 PROCESS FOR REFINING PRESSURE DISTILLATE David G. Brandt, Westfield, N. J., assigner to Cities Service Oil Company, New York, N. Y., a corporation of Pennsylvania Application October 23, 1937, Serial No. 170,518

(Cl. ISG-75) 4 Claims.

This invention relates to a process for refining cracked oil products and more particularly the cracked low boiling fractions which are to be used as motor fuels.

The cracking of petroleum oils for the production of gasoline causes the formation of various types of unsaturated hydrocarbons which are very desirable from the standpoint of increasing the antiknock value of the gasoline. Certain types of unsaturated hydrocarbons however tend to develop into gum forming constituents in the finished gasoline, and therefore cause considerable trouble. Various methods have been devised for the treatment and refining of cracked oil fractions both for the elimination of gums and for preventing the formation of gums in the finished gasoline.

The primary object therefore of the present invention is to provide a process for refining cracked oil fractions which will give -a motor fuel relatively stable with respect to gum formation.

A further object of the invention is to provide a process which is simple, inexpensive and easily carried out in existing apparatus.

In accordance with these objects, the process of the present invention comprises the intimate contacting and reacting of the low boiling point cracked oil fraction to be refined with a virgin petroleum distillate of higher boiling point such as gas oil, while in heated condition, and the separation of the refined cracked fraction from the resulting virgin distillate and undesired products of the reaction. The separation of the refined oil fraction from the mixture may be suitably eifected by distillation and rectification.

The detailed features of the process of the present invention, together with other objects, features and advantages, will best be understood from the following description taken in connection with the accompanying drawing in which:

The figure is a diagrammatic showing of apparatus which is suitably adapted for carrying out the improved process of the present invention.

Referring to the drawing, the cracked oil distillate to be refined which may be either treated or untreated distillate but preferably stabilized with respect to 10W boiling constituents, is introduced into the apparatus through a line 2 and forced by means of a pump 4 through a condenser preheater 6 in which the distillate is heated by indirect heat exchange with the vapors of the refined product produced in the process. The preheated distillate is then conducted through a line 8 into a mixing line I0 in which the preheated distillate is intimately mingled with relatively hot fresh virgin gas oil yor other virgin distillate of higher boiling point than the cracked distillate to be refined. The line Vlil may be as long as necessary to insure a thorough mingling and interaction between the cracked distillate and the straight run higher boiling :distillate.

The fresh gas oil or other straight run high boil-ing distillate to be used in the process is introduced into the apparatus through a line I2 and forced by means of a pump I4 through a line I6 and a series of heat exchangers I8 and 20. From the heat exchanger 20 the gas oil passes through a line 22 at a temperature of from 300 to 400 F. into the Vline Ill, where it is intimately mixed with the cracked distillate introduced thereinto. The resulting mixture reacts in the line I0 and passes into the lower midportion of -a combined fractionating and reaction tower 24.

A substantia1 portion of the cracked distillate is vaporized in the line I0 and in the tower 24 as it leaves the line I0. The unvaporized portion passes on to a series of trays below the line `I II where it comes in contact with relatively high temperature steam and vapors evolved in the lower part of the tower. All of the relatively heavy gasoline constituents desired in the final product are vaporized in the portion of the tower below the line I0 and pass with the previously vaporized material upwardly through the tower and are there rectified so that the desired cracked gasoline product is taken overhead from the tower through a vapor line 26 which serves to con-duct the vapors to the heat exchanger 6 referred to above. The partially cooled gasoline vapors are conducted through a line 28 and a cooler 30 in which the condensation of the vapors (and the steam) is completed. 'I'he resulting mixture flows through a line 32 into a water separator 34 from which the separated water is removed through a valved line 36. The rened gasoline is conducted from separator 34 through a line .38 into a receiver -40 and the finished product is withdrawn to storage through a valved line 4t2.

In the operation of the apparatus the end point of the overhead gasoline is preferably controlled by returning a sufficient proportion of the yfinished distillate to the upper part of the tower 24 to hold back the higher boiling constituents which are not desired in the gasoline. Accordingly, a portion of the gasoline distillate product is withdrawn from the receiver 40 through a line 44 and passed by means of a pump 46 through a valve controlled line 48 into the upper portion of the tower 24. The line 48 is provided with a thermostatically controlled valve 50 which is connected by means of wiring 52 to a thermostat 54 placed in the top of the tower 24.

The spent gas oil reaching the bottom of the tower 24 is withdrawn through a valved line 56 (preferably controlled by a oat in the bottom of the tower 24) and may be used directly as a cracking stock in a cracking operation. It may be conducted through a valved line 58 and the heat exchangers 2l) and I8 in succession from which the partially cooled gas oil is passed through a cooler 60 and discharged through a line 62. through the line 56 may be reheated land used for maintaining the desired relatively high temperature in the lower part of the tower 24. Spent gas oil for this purpose is withdrawn from the line 56 through a line 64 and forced by means of a pump 66 and a line 68 through a series of heating coils 1D mounted in a pipe still furnace 12. The spent gas oil heated to the desired temperature is conducted from the coil 'I0 through a transfer line 14 into the lower portion of the tower 24 where it is used to supply the heat for effecting the reaction with the cracked distillate and for maintaining the proper temperature for carrying out the rectification operation in the tower.

In the normal operation of the process as described there is a substantial proportion of the cracked distillate introduced into the tower 24 in the form of liquid which falls onto the lower trays of the tower. The heavy ends not desired in the nal product are retained by the gas-oil or other high boiling distillate along with the fixed gums and other heavy products of the reaction. Any relatively heavy constituents which have the proper boiling point to belong in the final product, and which may reach the bottom of the tower 24 are stripped from the liquid by the use of superheated steam introduced through a line 16 to a distributor 18. It is apparent in the operation of the tower 24 that certain portions of the gas oil or other distillate may be vaporized in the lower part of the tower, but such constituents along with the heavy ends of the cracked distillate and heavy reaction products will flow back down through the tower and finally be discharged with the spent gas oil through the line 56.

In carrying out the process of the present invention the proportion of virgin distillate introduced through the line l2 usually comprises approximately of the quantity of cracked product to be treated, but this proportion may vary from 5% to 20%, depending on the gumming characteristics of the cracked product to be treated.

The gas oil or other virgin distillate used in the process of the present invention for rening the cracked constituents may comprise any straight run heavy distillate fraction obtained directly from crude petroleum oil, but the oil used must be a virgin product and of higher boiling point than the cracked product to be treated. Many attempts have been made to carry out the refining operation of the present invention by the use of recycle and cracked gas oils, but such attempts have been completely unsuccessful. The reaction between the virgin A portion of the gas oil discharged gas oil and the cracked oil constituents is not definitely understood, but it appears that some definite reaction must take place between the gum forming constituents in the cracked products being treated and some particular constituents contained in the virgin distillate. Some natural constituent in the gas oil appears to react with the gum forming hydrocarbons of the cracked product because the oil soon becomes ineffective as a treating agent and must be discharged from the system. Regardless of what the reaction is, the treatment as effected by the improved process definitely produces a more gum stable finished gasoline than is otherwise obtained.

'Ihe refining of cracked oil distillates in accordance with the foregoing procedure has shown in general a reduction in the gum content of the distillate to approximately one tenth its original gum content. For example, cracked gasolines having copper dish gums of approximately 40 were changed so that the gum content was only from 4 to 6 ings. In the operation of the process the virgin gas oil acts as a gum carrier and a portion of the spent gas oil is preferably recirculated to supply the heat and temperature for the tower 26. This method of supplying heat avoids the use of indirect heating means and the consequent overheating of the cracked distillate. Furthermore, it avoids the necessity of using vacuum distillation in order to effect the rectification of the desired gasoline product. In the tower 24 the fresh gas oil or other distillate acts as a heat carrier and serves to shift the equilibrium in the rectification operation. l

The cracked gasolines subjected to the process of the present invention as stated above are preferably stabilized with respect to low boiling constituents so that no cracked gases are present. These gasolines may also have been previously subjected to the usual chemical treatment with sweetening agents, sulfuric acid, or clays.

Various modifications of the process may be made to adapt it for any particular problem, and it is obvious that the process may be carried out in various types of apparatus so long as the cracked products while in heated condition are brought in intimate contact with a virgin distillate of higher boiling point. For example, any suitable apparatus may be used in which a reaction zone is provided for intimately contacting cracked gasoline to be rened with `the virgin higher boiling distillate used as a refining agent. The cracked distillate may be heated to a temperature sufficient to vaporize all or a portion of its constituents prior to being brought in contact with the virgin distillate refining agent.

Having thus described the invention in its preferred form, what is claimed as new is:

l. The process of refining cracked petroleum distillates of the type of cracked gasoline having undesirable gum and gum-forming characteristics for the purpose of correcting such characteristics and for producing a refined cracked distillate of desired end point, which comprises continuously introducing the cracked distillate to be treated and a straight run virgin petroleum distillate of the type of gas oil of higher boiling point than the cracked distillate into a fractionating tower, said virgin distillate being introduced into said tower in the proportion of from 5% to 20% of the cracked distillate introduced thereinto, distilling and fractionating the cracked distillate in said tower in the presence of said virgin distillate which is partially vaporized in equilibrium with the constituents of said cracked distillate, continuously withdrawing overhead from the fractionating tower a rened cracked distillate of desired end point which is substantially free of gums and other heavy end products including constituents of said virgin distillate, and continuously withdrawing higher boiling virgin distillate together with gums and other heavy end products of the cracked distillate from the base of the fractionating tower and the process.

10 spect to low boiling constituents.

2. The process of rening as defined by claim 1 in which said cracked distillate is introduced into said fractionating tower while hot.

,i 3. The process of refining as dened by claim 1 in which said virgin distillate is introduced into said fractionating tower while hot.

4. The process of refining as defined by claim 1 in which said cracked distillate introduced into said fractionating tower is stable with re- DAVID G. BRANDT. 

